Key Takeaways & Executive Findings
- •• Igneous metamorphic coal exhibits enhanced spontaneous combustion tendency due to altered pore structure and oxygen consumption dynamics. • Oxidation reduces specific surface area and suppresses structure complexity increase, with effects more pronounced at higher metamorphic degrees. • Thermally metamorphic coal shows accelerated oxygen consumption, with oxidation amplifying differences in reaction rates compared to raw coal. • Pore structure evolution (increased volume/complexity, reduced uniformity/connectivity) synergistically enhances oxygen consumption capacity.
Abstract
In igneous-intruded coal seams, coal undergoes significant metamorphism, which critically alters its pore structure and oxygen consumption dynamics, thereby elevating its spontaneous combustion tendency. This study investigates the specific surface area, pore volume, structure complexity/connectivity, heterogeneity/local features of pore size distribution, and oxygen consumption dynamics of igneous metamorphic coal through N2/CO2 isothermal adsorption tests and low-temperature oxidation experiments, and elucidates the influence mechanisms of pore structure evolution on oxygen consumption dynamics during low-temperature oxidation. With increasing metamorphic degree, igneous metamorphic coal exhibits a more pronounced reduction in specific surface area during oxidation, while the increase in structure complexity due to coal-oxygen reactions is suppressed. Thermally metamorphic coal demonstrates accelerated oxygen consumption, with oxidation amplifying the difference in reaction rates compared to raw coal. Key mechanisms include oxidation-induced reduction in mesopore complexity and micropore volume, decreased dominance of small-pore-volume apertures, and increased heterogeneity, collectively leading to a lower half-oxygen-consuming temperature and steeper oxygen consumption curves. Simultaneously, increased pore volume/complexity and reduced uniformity/connectivity act synergistically to enhance oxygen consumption capacity, highlighting the coupling between pore structure evolution and oxidation behavior in igneous metamorphic coal. This study provides theoretical insights into the pore-oxygen coupling mechanisms governing coal spontaneous combustion in igneous intrusion areas.
1. Introduction
Coal in igneous-intruded areas undergoes pronounced metamorphism under thermal and stress effects, rapidly transforming low-rank coal into medium- to high-rank coal or even natural coke [1,2]. In China, igneous intrusions into coal seams are widely observed in major coal-producing regions such as Liaoning, Anhui, and Shanxi [3]. The unique metamorphic characteristics of coal significantly enhance their spontaneous combustion tendency, leading to frequent fire incidents in goafs within igneous intrusion areas, which pose severe risks to coal mine safety [4].
Magma intruding into coal seams constitutes a high-temperature, non-steady process dominated by heat conduction, generating geothermal anomalies that induce thermal metamorphism [5]. Direct contact between magma and coal further causes severe metamorphism, forming high-rank metamorphic coal or natural coke. Compared to conventionally metamorphic coal (such as dynamically metamorphic coal), the pore structure in IMC exhibits fundamental differences. The pore evolution of conventionally metamorphic coal is primarily influenced by slow geological stress effects, resulting in predominantly uniformly developed pore structures [6]. In contrast, IMC undergoes rapid pyrolysis and contact metamorphism during high temperatures and pressures, non-steady-state processes associated with magmatic intrusion [7]. It leads to the formation of highly heterogeneous pore structures, significantly influencing oxygen diffusion and reaction kinetics. This difference may cause IMC to exhibit different oxidation behaviors, necessitating a detailed investigation into the pore-oxygen coupling mechanisms.
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Xu Shao, Botao Qin, Quanlin Shi, Ziwei Li, Bao Qu, Shibo Xu, Junyu Wang, Mingyue Weng (2026). Influence mechanism of pore structure evolution on oxygen consumption dynamics during low-temperature oxidation of igneous metamorphic coal. SinoTechIntel Verified Research. https://doi.org/10.1016/j.ijmst.2026.01.001
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Frequently Asked Questions
What is igneous metamorphic coal?
Igneous metamorphic coal (IMC) is coal that has undergone metamorphism due to the thermal and stress effects of igneous intrusions, transforming it into higher-rank coal or natural coke, with distinct pore structures and oxidation characteristics.
How does pore structure evolution affect oxygen consumption in igneous metamorphic coal?
Pore structure evolution, including changes in pore volume, complexity, and connectivity, directly influences oxygen diffusion and reaction kinetics. Increased pore volume and complexity, along with reduced uniformity, enhance oxygen consumption capacity, accelerating spontaneous combustion.
What methods were used in this study?
The study employed N2/CO2 isothermal adsorption tests to characterize pore structure and low-temperature oxidation experiments to measure oxygen consumption dynamics, along with analyses of specific surface area, pore volume, and pore size distribution.
Why is igneous metamorphic coal more prone to spontaneous combustion?
Igneous metamorphic coal exhibits accelerated oxygen consumption due to its unique pore structure evolution, which enhances oxygen accessibility and reactivity, leading to a lower half-oxygen-consuming temperature and steeper oxygen consumption curves, increasing spontaneous combustion risk.
What are the practical implications of this research?
The findings provide theoretical insights into the pore-oxygen coupling mechanisms governing coal spontaneous combustion in igneous intrusion areas, aiding in the development of targeted prevention and control strategies for coal mine fires.
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